Various methods are known for improvement of humidity resistance and dielectric properties at a high frequency region in epoxy resin composition, polyimide resins and like resins, and for improvement of heat resistance and solvent resistance of polyolefin resins, polyphenylene ether resins and like as insulating materials: for example, curing by sulfur, organic peroxide, or crosslinking by electronic ray, radioactive ray of copolymers of ethylene and a norbornene type monomer (JP-A-62-34924); and use of a polyphenylene ether substituted by a propargyl or allyl group, a polyphenylene ether containing a double bond, and a polyphenylene ether modified by an unsaturated carboxylic acid or acid anhydride thereof (JP-A-1-69628, JP-A-1-69629, JP-A-1-113425, JP-A-1-113426, JP-A-1-239017, etc.).
However, in the former method, the dielectric constant is as high as 3.7 or more, and therefore the former method is not suitable for use as insulating materials such as overcoat materials and interlayer insulation materials.
On the other hand, in the latter examples, an allyl group, olefinic unsaturated group, or unsaturated carboxylic acid is used as a curable functional group, which results in insufficient heat resistance because of insufficient curing reactivity, especially in an oxygen atmosphere (in air).
The object of the present invention is to provide an insulator having excellent thermal shock resistance and excellent dielectric properties, and a suitable material therefor.